The instant invention is in the field of eyeglass tinting machines which are used to make either a solid or a gradient tint on prescription eyeglass lenses, generally plastic lenses.
Immersion of the eyeglass lenses completely into the dye solution in a dye vat for a period of time will produce a solid tint, the color density of which is a function of the immersion time. Another type of tint, called the gradient tint, begins with a clear lens (at the bottom), and then gradually increases in color density toward the top where the density is the greatest. As with solid tints, the density of gradient tints is a function of immersion time.
However, the relationship between density and immersion time is non-linear because the lenses absorb faster at the beginning of their tinting cycle than at the end. Because of this nonlinearity, creating a good gradient tint was once a problem. At one time an even gradient could only be achieved by manual immersion. Thereafter, simple machines were developed to produce gradient tints, but these machines were not very efficient or effective until in recent years, in which manufacturers began incorporating microprocessors into the systems to more carefully control the dipping action.
These systems typically have a fairly complicated set of controls with a keyboard and a digital read-out. The keyboard must be used to enter the depth of the gradient in millimeters, and other parameters require digital entry in order to operate the machine.
Even beyond the relative complexity of operation of these machines, they still tended to make blotchy and streaked lenses, particularly when making a gradient tint. If the lenses are stationary in the hot dye in which they are tinted for any length of time, unless they are complete immersed, there will be a line or streak at the dye water line. When such streaks are made, the operator will then try to bleach them out by dipping them in a bleach solution, and then re-dye them to darken them up again. Not only is this tedious, but also ineffective as the streaks are generally not ever completely removed.
In addition to streaks caused in this manner, blotching, smeared, and streaked appearances of the tinted lenses is also caused by the non-uniform nature of the solution of dye. The non-uniformity takes two forms. First, the dye density varies somewhat at a very local level, so that certain places of the lenses may be darker than other because they were exposed to higher color density zones in the dye. Typically, the dye is a "dispersible" which will tend to settle out of dispersion if left still, rather than being a completely soluble solution. Additionally, because the dye is typically heated from the bottom and sides, there is a circulation caused by the heating which also helps make the heat uniform within the vat of dye. Nonetheless, the mere fact that there is circulation is evidence that some areas are hotter than others, and the hotter the dye is, the faster it is to "take" on the lens.
For these reasons, a lens, whether it be tinted solid or with a gradient, will not have a uniform appearance or an even gradient appearance, as the case may be, if it immersed in the dye partially or wholly and left stationary for any period of time. It must be continually in motion to both stir the dye right at the surface of the lenses, and expose the surfaces of the lenses to continuously changing portions of the dye to even out absorption disparity caused by temperature gradient or color density gradient within the dye itself.